The present invention relates to an AC evaluation equipment for checking if a signal generator and a digitizer used in an analog testing part of an IC tester are within predetermined tolerances.
In an IC tester a signal generator and a waveform analyzer are occasionally checked to see if they are still within predetermined tolerances; namely, they are subjected to an AC evaluation. If they are not within the tolerances, that is, if they are found degraded, they are repaired for accurate testing. The waveform analyzer which is usually called digitizer periodically samples an input waveform signal, converts each sample value into digital data, and subjects the data to a fast Fourier transform, then outputs the frequency components of the input waveform signal and their levels.
FIG. 1 shows a conventional arrangement for AC evaluation for the IC tester. An analog testing part 100 of the IC tester includes a plurality of AC signal generators 11 and 24, a DC voltage generator 21, a clock signal generator 17, a digitizer 15, a test processor 18, besides a voltage measurement unit (not shown) which are used primarily for analog testing of IC's. For the AC evaluation of the AC signal generator 11 or the digitizer 15 in the analog testing part 100, a standard signal generator 16, precision low-frequency and high-frequency voltage measurement units 12 and 13, and a distortion-factor meter 14 are provided outside of the analog testing part 100 and connected thereto. For example, the AC signal generator 11 to be evaluated in the analog testing part 100 is caused to generate an AC signal, which is measured by the low-frequency or high-frequency AC voltage measurement unit 12 or 13, depending on whether the AC signal is low-frequency or high-frequency, to see if the AC signal generator 11 outputs an AC signal of a predetermined amplitude within a given tolerance. Furthermore, the AC signal from the AC signal generator 11 is applied to the distortion-factor meter 14, by which the amplitudes of the fundamental wave and respective harmonics of the AC signal are measured and the ratio between the amplitudes of the fundamental wave and the highest harmonic is obtained as a distortion factor (i.e. the dynamic range or the frequency purity) to see if the dynamic range of the AC signal generator 11 is in excess of a predetermined value.
Next, an AC signal of a frequency, preset based on a clock signal, is applied from the standard signal generator 16 to the digitizer 15 to be evaluated in the analog testing part 100 of the IC tester. The accuracy of the AC level of the digitizer 15 is evaluated from its fundamental wave output level with respect to the input AC signal level and its dynamic range is evaluated from the ratio between the fundamental wave output level and a maximum output level of the other frequency components (or noise). Then, the standard signal generator 16 is caused to generate an AC signal of a different frequency and the corresponding output level of the digitizer 15 is measured to evaluate its frequency characteristic (i.e. flatness). During these measurements a clock signal of a reference frequency is supplied from the clock signal generator 17 to the standard signal generator 16 and the digitizer 15 to thereby synchronize the frequency of the AC signal from the standard signal generator 16 with the sampling frequency of the digitizer 15.
The low-frequency AC voltage measurement unit 12, the high-frequency AC voltage measurement unit 13, the distortion-factor meter 14, and the standard signal generator 16 are all high precision units calibrated according to the national standards, and hence they are costly. These devices are not needed for the IC test which is the primary object of the IC tester and they are used only for the evaluation of the AC signal generator 11 and the digitizer 15 in the analog testing part 100. In the case of evaluating them, the above-mentioned measurement units are placed under control of the test processor 18 via a GP-IB bus 19. However, since the GP-IB bus 19 is low-speed, the evaluation consumes much time, during which the IC tester has to be stopped from its test operation. In addition, the evaluation must be done periodically--this inevitably impairs the efficiency of utilization of the IC tester.